What’s the difference between memory (RAM) and hard disk space?

There are two things that people refer to as "memory" and they are very commonly confused. However, they mean two entirely different things so it's important to understand the difference.

Most people have between 64 megabytes (64MB) and 512 megabytes (512MB) of Random Access Memory (RAM) fitted inside their PC. This is a small but very fast area of memory in the system for the files and data that your system is using at this point in time. As you open documents, pictures, programs, etc on your system, they take up more of the available RAM. When you close them, they delete themselves out of RAM, making your system more responsive to the files that you want to use next by having RAM spare for use by the files that you are about to use. This is the true meaning of the word "memory" in most conversations. For example, a "memory" upgrade is upgrading from 64MB of RAM to 128MB of RAM, etc.

Most people have between 6 gigabytes (6GB) and 80 gigabytes (80GB) of hard disk capacity and between 1GB and 60GB of free space on the hard disk. One gigabyte is approximately 1000 megabytes (1,024Mb to be exact). Therefore, 10 gigabytes is approximately 10,000 megabytes. As you can see, that's vastly different to the amount of RAM that is fitted inside PCs. Your hard disk space is where all of your programs, documents, pictures and other data are saved inside your PC, even if you’re not using them at this point in time - that's why they don't get forgotten when you unplug the power from your system.

I won't go into the technicalities of what "virtual memory" is here as that will confuse almost any novice but it's enough to say that you do need to keep a bit of space free on the hard disk, partly to be able to save new files but also to be able to keep your system running efficiently. 200Mb is about the minimum that you should have available on most Windows 98 and Windows ME systems and 500Mb is about the minimum amount of free disk space for most Windows 2000 and Windows XP PCs and laptops.